Blowing lance nozzle

ABSTRACT

The invention concerns a blowing lance nozzle ( 1 ) comprising: a central tube ( 2 ) supplying stirring gas, an inner tube ( 5 ) for intake of a cooling liquid, an outer tube ( 10 ) for evacuation of the cooling liquid, a heat exchanging space ( 13 ), and outlet conduit ( 15 ) for the stirring gas exiting from each orifice ( 4 ) in the front wall ( 3 ), the front wall ( 12 ) having a central recess ( 16 ) which is oriented towards the central orifice ( 8 ) and has a recess height/recess base ratio not less than 0.35, said heat exchanging space having a section for allowing through the cooling liquid through said space which is substantially constant, so as to obtain a cooling liquid passage speed through said space which is more or less constant.

[0001] The present invention relates to a blow-lance nose intended forstirring baths, comprising

[0002] a central tube for supplying stirring gas, closed at one endturned towards the bath by a first front wall provided with at least oneopening,

[0003] an internal tube forming with the central tube a first annularcavity for the passage of a cooling liquid and closed at one end turnedtowards the bath by a second front wall having a central opening and onepassage orifice per opening provided in the said first front wall,

[0004] an external tube forming with the internal tube a second annularcavity for the passage of the cooling liquid and closed at one endturned towards the bath by a third front wall having one outlet orificeper opening provided in the said first front wall,

[0005] a heat exchange space which is situated between on the one handthe said second front wall and the said third front wall and on theother hand the said central opening and the said second annular cavity,and in which the cooling liquid flows, and

[0006] an outlet conduit for the stirring gas leaving each opening inthe said first front wall and going as far as an aforementionedcorresponding outlet orifice, passing through an aforementionedcorresponding passage orifice in a manner which is impervious to thecooling liquid.

[0007] Blow-lance noses of this type have been known for a long time.The blow-lance noses described in EP-A-0 340 207, WO-97/000973 and U.S.Pat. No. 4,432,534 can be cited by way of examples.

[0008] In order to stir steelworks converter baths with oxygen jets, thelance noses operate at a distance of 1 to 2.5 m from the bath whilst thebath has a temperature of around 1400° C. Under these operatingconditions, the temperature of the nose can increase rapidly to 400° C.and must remain in this environment for approximately 20 minutes. Then,when the lance is withdrawn, the nose rapidly returns to ambienttemperature, that is to say 20° C.

[0009] Provision is therefore made for constructing the front walls ofthe lance noses from a material which is a very good conductor of heat,for example copper, to allow an effective as possible heat exchange witha cooling liquid which flows at great speed along this wall, inside thenose. However, the lance noses already known have the drawback ofoffering cooling which is not uniform over the entire surface of thiswall exposed to variations in thermal conditions which are extremelycritical. This results in mechanical tensions between the various areasof the wall.

[0010] Moreover, cavitation phenomena are frequently observed in thecooling liquid following local pressure drops therein. This cavitationhas the effect of causing poor cooling between the cooling liquid andthe wall to be cooled, the heat exchangers being much less good betweena gaseous phase and a solid phase than between a liquid phase and asolid phase.

[0011] Many attempts have been made to smooth out the flow of thecooling liquid inside the lance nose, for example by forming slightdepressions in the external front wall of the nose (see for example U.S.Pat. No. 4,432,534 and WO 96/23082). These arrangements do however havethe drawback of not offering sufficient heat exchange surface, inparticular in the central area of the nose.

[0012] There is also provided, in the central area of the lance nosedescribed in EP-A-0340207, a large depression onto which secondary jetsof cooling liquid are directed, which has the effect of causingturbulence in the liquid flow.

[0013] The aim of the present invention is to propose a lance nose whichis capable of sustaining the high stresses to which it is subjected,during a significant number of successive uses, whilst providing a lancenose which is simple to manufacture and of justifiable cost.

[0014] This problem is resolved, according to the invention, by ablow-lance nose as described at the start, in which the said third frontwall has a central depression which is directed towards the said centralopening and which has a ratio between height of depression and base ofdepression equal to or greater than 0.35, and the aforesaid heatexchange space has a cross-section for the passage of the cooling liquidwhich is substantially constant, so as to obtain a speed of passage ofthe cooling liquid through this space which is approximately constant,in the presence of the said depression.

[0015] Through such a depression, the heat exchange surface increasesgreatly compared with an identical surface of the heat front coming fromthe bath, without causing any turbulence or cavitation in the liquid.Advantageously, the said central depression has a ratio between heightand base equal to or greater than 0.4, in particular 0.5, andpreferentially even 0.8.

[0016] The expression “cross-section for the passage of cooling liquid”means that the cross-sections referred to are taken perpendicular to thedirection of flow of the cooling liquid in the heat exchange space.

[0017] In this way, at a constant flow rate, the flow rate/cross-sectionratio remains constant and therefore the speed of passage of the liquidalso remains constant. It can thus be ensured that, at a given passagespeed, and at the critical temperature of the front wall to be cooled,there is no risk of any cavitation phenomenon occurring in the coolingliquid, which in general is water. Advantageously, for the front walltemperatures indicated above, a passage speed of the liquid flow ofbetween 8 and 12 m/sec will be provided.

[0018] Substantially constant cross-section means, according to theinvention, that the surface area of this cross-section cannot varywithin limits greater than 10%.

[0019] According to one embodiment of the invention, the lance nosecomprises several aforementioned passage conduits disposed around acentral axis and the said central depression extends from the saidoutlet orifices of these conduits. The base of the depression is thusadvantageously maximal and affords improved efficacy of the heatexchange in the depression. In an improved manner, the third front wallhas an outside diameter and the base of the said depression is a circlehaving a diameter equal to at least 0.25× the said external diameter,preferably at least 0.33× this outside diameter. The central depressionis thus according to the invention in no way a small central hollowprovided in the wall of the nose in order to reinforce the rigiditythereof.

[0020] According to one advantageous embodiment of the invention, thesaid third front wall has a central depression in the form of a cone.

[0021] According to an improved embodiment of the invention, the saidsecond front wall has, around the central opening, a central deformationin the form of a truncated cone which is directed towards the said firstfront wall. The said cone and the said truncated cone preferably have acommon axis and the central depression in the form of a cone forms withthis axis an angle greater than the angle formed between this axis andthe central deformation in the form of a truncated cone. In this way,even in the heat exchange space situated between the central depressionof the third front wall and the central deformation of the second frontwall, the cross-section can remain constant and the speed of passage ofthe flow liquid remains there too equivalent to that obtained along theentire third front wall.

[0022] According to a particular embodiment of the invention, thecentral depression is covered at least partially with a protectivescreen made from a material with high thermal resistance. This may be aplate in the form of a disc which is carried by the central depressionor clamped against it and which therefore requires no welding to fix it.The heat exchange between the cooling liquid and the third front wallremains unchanged, whilst a major part of the surface area of the thirdfront wall is sheltered from excessive overheating.

[0023] Other embodiments of the lance nose according to the inventionare indicated in the accompanying claims.

[0024] Other details and particularities of the invention will emergefrom the description given below, non-limitingly, of example embodimentsof the invention, and making reference to the accompanying drawings.

[0025]FIG. 1 depicts a view in axial section of a blow-lance noseaccording to the invention.

[0026]FIG. 2 depicts a view in axial section of a variant embodiment.

[0027]FIG. 3 depicts a detail of a lance nose according to the inventionfor illustrating the method of measuring the parameters necessary to theinvention.

[0028] In the various drawings, the identical or similar elements aredesignated by the same references.

[0029]FIG. 1 depicts a blow-lance nose 1. This nose comprises a centraltube 2 for supplying stirring gas. This central tube 2 is closed by afront wall 3 which, in the example illustrated, is provided with severalopenings 4.

[0030] An internal tube 5 is arranged coaxially around the central tube2 and these tubes form between them an annular cavity 6 which, in theexample illustrated, serves to supply cooling water in the direction ofthe arrow F₁. This internal tube 5 is closed by a front wall 7 which isreferred to as a separator. This front wall 7 is provided with a centralopening 8 and an orifice 9 in line with each opening 4 in the centraltube 2.

[0031] An external tube 10 is arranged coaxially around the central tube2. This external tube is generally made from steel and forms with theinternal tube 5 an annular cavity 11 which, in the example illustrated,serves for discharging cooling water in the direction of the arrow F₂.This external tube 10 is closed by a front wall 12 which faces the bathto be stirred and which is therefore subjected to critical heatstresses, as explained above. Advantageously this front wall is madefrom a material which is a good conductor of heat, for example copper,to allow a heat exchange which is as effective as possible between theheated front wall 12 and the cooling water passing through the heatexchange space 13 which is situated between the front wall 7 of theinternal tube 5 and the front wall 12 of the external tube 10. In theexample embodiment illustrated, the cooling water coming from the cavity6 passes through the central opening 8 in the heat exchange area 13.There it flows in the direction of the arrow F₃ towards the outside,that is to say towards the cavity 11.

[0032] The front wall 12 is also provided with an outlet orifice 14 inline with each opening 4 provided in the front wall 3 and with eachpassage orifice 9 provided in the front wall 7. In each of these alignedorifices and openings there is arranged an outlet conduit 15 for theejection of stirring gas outside the lance nose. These conduits areadvantageously produced from an erosion-resistant material, for examplebronze, and are directed obliquely with respect to the axis 9 of thelance nose.

[0033] As is clear from the example embodiment illustrated, the externalfront wall 12 is, according to the invention, provided at its centrewith a depression 16 in the form of a cone, which is directed towardsthe central opening. This depression is preferably sufficientlypronounced to have a ratio between the height of the internal wall ofthe cone (h) and the base diameter (B) equal to or greater than 0.35. Inthe case illustrated this ratio is equal to approximately 0.5. In thisway, the heat exchange area 13 is greatly increased for the same heatfront to which the lance nose is subjected, and hence an increasedefficacy in the cooling of the front wall 12. It is entirelyadvantageous, as depicted, that this depression 16 extends from theoutlet conduits 15 and therefore forms a cone whose base is maximal. Inthe example illustrated, the ratio between the base B of the depressionand the outside diameter D of the front wall 12 is approximately 0.33.Moreover, through the deep depression, the central area of the externalfront wall, which is thermally the most stressed, is separated to themaximum possible extent from the surface of the bath.

[0034]FIG. 3 illustrates how the parameters h and B of the lance noseaccording to the invention must be measured.

[0035] The height h is calculated between on the one hand the bottomtangent plane 30 of the lance nose perpendicular to the axis 19 and theparallel plane 31 tangent to the top of the depression. If an elementforeign to the depression is provided at the top thereof, such as forexample the tie rod 20 in FIG. 2, the plane 31 remains in the positionwhich it would have if this foreign element did not exist. The top ofthe depression must then be considered to be a virtual point to be takeninto account in the measurement.

[0036] The base B is situated in the bottom tangent plane 30. It iscircumscribed by the line 32 resulting from the intersection betweenthis plane 30 and the extension 33 of the internal faces 34 of thedepression. Account is therefore not taken of the rounded parts.

[0037] As can be seen in FIG. 1, the outside diameter of the front wall12 is taken where its value is maximal.

[0038] The front wall 7, serving as a separator between the water supplyand the water outlet, also has a central deformation 17 directed towardsthe front wall 3. This deformation 17 has the shape of a truncated coneopen towards the top through the central opening 8.

[0039] This truncated cone 17 is coaxial with the cone formed by thedepression 16, their common axis being the axis 19 of the lance nose.The cone of the depression 16 forms with the axis 19 an angle largerthan the angle formed between this axis and the imaginary extension ofthe truncated cone 17 as far as this axis.

[0040] As a result the truncated cone 17 is further away from the cone16 at its apex than at its base. However, at its apex, the truncatedcone is narrower. Therefore, the cross-section of the heat exchangespace situated between the front walls 7 and 12, which is measured in aplane perpendicular to the direction of flow of the cooling liquid,remains constant even in the presence of the central depression 16provided in the example embodiment illustrated in FIG. 1.

[0041] Moreover, at the outlet conduits 15, the cooling liquid can passonly through the interstices situated circumferentially between theseconduits in the heat exchange space 13. Consequently, in order tomaintain at this point a constant cross-section of flow for the coolingliquid and therefore a constant speed of flow at a given flow rate, aninward bulge 18 in the front wall 7 serving as a separator is providedin each of the aforesaid interstices.

[0042] The lance nose according to the invention is therefore arrangedso as to provide over the entire extent of the heat exchange area 13 aconstant cross-section of flow for the cooling liquid. At a given flowrate of the water supply there is obtained a ratio between this flowrate (d) and the cross-section (S) which remains constant during thefunctioning of the lance, this ratio corresponding to a speed of passageof the flow liquid expressed in m/sec. Advantageously, the flow rate andthe cross-section will be determined so as to obtain a speed of flowwhich is approximately constant and between 8 and 12 m/sec. Thephenomenon of cavitation can thus be avoided to the maximum possibleextent, which greatly improves the efficacy of the heat exchangeobtained in the nose.

[0043] In the example embodiment illustrated in FIG. 2, a lance nose isdepicted which is differentiated from the one depicted in FIG. 1 by thefact that the depression 16 is more pronounced. The top of thedepression 16 projects through the opening 18 and therefore even emergesin the space between the front walls 3 and 7, which makes it possible toobtain a ratio of h to B equal to or greater than 0.8. In order betterto ensure the mechanical strength of the depression 16, it is possibleto provide a retaining element, for example a tie rod 20, between thetop of the depression and a nut arranged on or in the front wall 3 ofthe central tube 2.

[0044] Moreover, the central depression 16 is, in this exampleembodiment, completely covered with a heat-resistant plate 21. In thisway, whilst allowing unchanged heat exchange between the cooling waterand the cone formed by the depression 16, the central part of the lancenose is thermally insulated from the heat in the bath, which increasesthe efficacy of the heat exchange and affords a longer service life forthe lance nose.

[0045] In the example embodiment illustrated in FIG. 2, the plate 21 iscomposite, that is to say it has an external layer made from arefractory material, for example ceramic, or refractory steel, and aninternal layer made from a thermally insulating material such as forexample fibrous alumina.

[0046] In the example illustrated, this plate is simply clamped betweenthe head 22 of a threaded rod 23 passing through the plate 21 andscrewed into a thread provided in the head of the tie rod 20. Othermethods of fixing this plate could of course be provided.

[0047] Comparative tests were carried out under the same conditions inbaths in a steelworks.

[0048] The tests were carried out with conventional noses from threecompeting firms (Tests I to III in the table below), noses manufacturedby the applicant with a slight central depression where the ratioh/B=0.15 and the ratio D/B=0.15 (Test IV) and noses according to theinvention where the ratio h/B=0.44 and the ratio D/B=0.30 (Test V).TABLE Tests I II III IV V Mean service life 130 130 223 282 366

[0049] The service life of a nose is calculated on the number of castswhich it has been possible to stir before having to scrap this nose. Ascan be seen from this table, the improvement in the mean service life ofthe noses according to the invention is remarkable and completelyunexpected.

[0050] It must be understood that the present invention is in no waylimited to the embodiments described above and that many modificationscan be made thereto without departing from the scope of the accompanyingclaims.

1. Blow-lance nose (1) intended for stirring baths, comprising a centraltube (2) for supplying stirring gas, closed at one end turned towardsthe bath by a first front wall (3) provided with at least one opening(4), an internal tube (5) forming with the central tube a first annularcavity (6) for the passage of a cooling liquid and closed at one endturned towards the bath by a second front wall (7) having a centralopening (8) and one passage orifice (9) per opening (4) provided in thesaid first front wall (3), an external tube (10) forming with theinternal tube (5) a second annular cavity (11) for the passage of thecooling liquid and closed at one end turned towards the bath by a thirdfront wall (12) having one outlet orifice (14) per opening (4) providedin the said first front wall (3), a heat exchange space (13) which issituated between on the one hand the said second front wall (7) and thesaid third front wall (12) and on the other hand the said centralopening (8) and the said second annular cavity (11), and in which thecooling liquid flows, and an outlet conduit (15) for the stirring gasleaving each opening (4) in the said first front wall (3) and going asfar as an aforementioned corresponding outlet orifice (14), passingthrough an aforementioned corresponding passage orifice (9) in a mannerwhich is impervious to the cooling liquid, characterised in that thesaid third front wall (12) has a central depression (16) which isdirected towards the said central opening (8) and which has a ratiobetween height of depression and base of depression equal to or greaterthan 0.35, and in that the aforesaid heat exchange space (13) has across-section for the passage of the cooling liquid which issubstantially constant, so as to obtain a speed of passage of thecooling liquid through this space which is approximately constant, inthe presence of the said depression.
 2. Lance nose according to claim 1,characterised in that it comprises several aforementioned passageconduits (15) disposed around a central axis (19) and in that the saidcentral depression (16) extends from the said outlet orifices (14) ofthese pipes.
 3. Lance nose according to claim 2, characterised in thatthe third front wall has an outside diameter and in that the base of thesaid depression is a circle having a diameter equal to at least 0.25×the said external diameter.
 4. Lance nose according to one of claims 1to 3, characterised in that the said second front wall (7) has, aroundthe central opening (8), a central deformation (17) in the form of atruncated cone, which is directed towards the said first front wall (3).5. Lance nose according to claim 4, characterised in that the centraldepression (16) has the shape of a cone, in that the said cone and thesaid truncated cone have a common axis (19) and in that the centraldepression (16) in the form of a cone forms with this axis an anglegreater than the angle formed between this axis and the centraldeformation (17) in the form of a truncated cone.
 6. Lance noseaccording to any one of claims 1 to 5, characterised in that the centraldepression (16) projects through the central opening (8) towards thesaid first front wall (3).
 7. Lance nose according to any one of claims1 to 6, characterised in that it comprises a retaining element (20)which fixes a top of the central depression (16) to the said first frontwall (3).
 8. Lance nose according to any one of claims 1 to 7,characterised in that the central depression (16) is at least partiallycovered with a protective screen (21) made from a material with highthermal resistance.
 9. Lance nose according to claim 8, characterised inthat the protective screen (21) is carried on a rod (23) fixed to thetop of the central depression (16).
 10. Lance nose according to any oneof claims 1 to 9, characterised in that it comprises severalaforementioned passage conduits (15) separated circumferentially byinterstices, and in that the said second front wall has at eachaforementioned interstice a bulge (18) directed inwards.
 11. Lance noseaccording to any one of claims 1 to 10, characterised in that it has aratio between the depression height and the depression base equal to orgreater than 0.4, advantageously 0.5, preferably 0.8.
 12. Lance noseaccording to any one of claims 1 to 11, characterised in that the heatexchange space (13) is supplied with water at a predetermined flow rateand in that it has a ratio between this flow rate and the saidcross-section $\left( \frac{d}{S} \right)$

giving rise to a speed of passage of the flow liquid of between 8 and 12m/sec.